How the Tesla Turbine Works

Tesla, as well as many contemporary scientists and industrialists, believed his new turbine to be revolutionary based on a number of attributes. It was small and easy to manufacture. It only had one moving part. And it was reversible.

To demonstrate these benefits, Tesla had several machines built. Juilus C. Czito, the son of Tesla's long-time machinist, built several versions. The first, built in 1906, featured eight disks, each six inches (15.2 centimeters) in diameter. The machine weighed less than 10 pounds (4.5 kilograms) and developed 30 horsepower. It also revealed a deficiency that would make ongoing development of the machine difficult. The rotor attained such high speeds -- 35,000 revolutions per minute (rpm) -- that the metal disks stretched considerably, hampering efficiency.

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In 1910, Czito and Tesla built a larger model with disks 12 inches (30.5 centimeters) in diameter. It rotated at 10,000 rpm and developed 100 horsepower. Then, in 1911, the pair built a model with disks 9.75 inches (24.8 centimeters) in diameter. This reduced the speed to 9,000 rpm but increased the power output to 110 horsepower.

Bolstered by these successes on a small scale, Tesla built a larger double unit, which he planned to test with steam in the main powerhouse of the New York Edison Company. Each turbine had a rotor bearing disks 18 inches (45.7 centimeters) in diameter. The two turbines were placed in a line on a single base. During the test, Tesla was able to achieve 9,000 rpm and generate 200 horsepower. However, some engineers present at the test, loyal to Edison, claimed that the turbine was a failure based on a misunderstanding of how to measure torque in the new machine. This bad press, combined with the fact that the major electric companies had already invested heavily in bladed turbines, made it difficult for Tesla to attract investors.

In Tesla's final attempt to commercialize his invention, he persuaded the Allis-Chalmers Manufacturing Company in Milwaukee to build three turbines. Two had 20 disks 18 inches in diameter and developed speeds of 12,000 and 10,000 rpm respectively. The third had 15 disks 60 inches (1.5 meters) in diameter and was designed to operate at 3,600 rpm, generating 675 horsepower. During the tests, engineers from Allis-Chalmers grew concerned about both the mechanical efficiency of the turbines, as well as their ability to endure prolonged use. They found that the disks had distorted to a great extent and concluded that the turbine would have eventually failed.

Even as late as the 1970s, researchers had difficulty replicating the results reported by Tesla. Warren Rice, a professor of engineering at Arizona State University, created a version of the Tesla turbine that operated at 41 percent efficiency. Some argued that Rice's model deviated from Tesla's exact specifications. But Rice, an expert in fluid dynamics and the Tesla turbine, conducted a literature review of research as late as the 1990s and found that no modern version of Tesla's invention exceeded 30 to 40 percent efficiency.

This, more than anything, prevented the Tesla turbine from becoming more widely used.

As the Office of Naval Research in Washington, D.C., plainly stated: "The Parsons turbine has been around a long time with entire industries built around it and supporting it. If the Tesla turbine isn't an order of magnitude superior, then it would be pouring money down the rat hole because the industry isn't going to be overturned that easily …" [source: Cheney].

So, where does that leave the Tesla turbine today? As we'll see in the next section, engineers and automotive designers are once again turning their attention to this 100-year-old technology.